Synthesis and characterization of trinuclear copper-pyrazolate complexes: Their redox activity and systematic assembly of polynuclear complexes

In this work, a study towards the isolation of new triangular copper(II) complexes of general formula [Cu3(mu3-E)(mu-4-R-pz)(XX'X")] and polynuclear complexes containing [Cu3(mu3-E)]-moieties has been carried out. These trinuclear complexes are potential models for the active sites of several multicopper enzymes.;New triangular Cu(II)-pz complexes: [Cu3(mu3-OH)(mu-pz) 3(py)3](CF3SO3)2, [Cu 3(mu3-OH)(mu-4-Cl-pz)3(py)3](CF 3SO3)2, [Cu3(mu3-OH)(mu-4-Br-pz) 3(py)3](CF3SO3), (TBA)[Cu3(mu 3-OH)(mu-pz)3(NCS)3], (TBA)2[Cu 3(mu3-Cl)2(mu-pz)3(NCS)2Cl], and [Cu3(mu3-OH0.5)(mu3-pz) 3(pzH)3](CF3SO3)1.5 have been synthesized and characterized. In addition, complexes of higher nuclearities [{Cu 3(mu3-OH)(mu-4-NO2-pz)3(py) 2}3(mu3-NO3)](CF3SO 3)5·4H2O, (TBA)2[Cu4(mu-OH) 2(mu-pz)4Cl4], and [Cu12(mu 3-OH)6(mu-pz)16(NCO)2]·4H 2O have been isolated while working in the synthesis of the latter trinuclear complexes. Besides the isolation and characterization of these new complexes, this study highlights the importance of the choice of starting materials while targeting complexes with a variety of terminal ligands. It also provides evidence that the presence of appropriate terminal ligands, X, is a requirement for the stabilization of [Cu3(mu3-E)(mu-pz)3X 3]-complexes.;Efforts toward the synthesis of polynuclear complexes with two closely-spaced Cu3(mu3-E)-units held together by pyrazolate ligands were pursued providing new ligands and complexes: N, N'-bis-(1H-pyrazol-4-ylmethylene)-butane-1,4-diamine, and (1H-pyrazol-4-ylmethylene)-(3-{[(1H-pyrazol-4-ylmethylene)-amino]-methyl}-benzyl)-amine, (TBA)2[Cu3(mu3-Cl)2(mu-4-CO 2Et-z)3Cl3], (PPN)3[Cu3(mu 3-Cl)2(mu-4-CHO-pz)3Cl3]CI, (PPN)[{Cu 3(mu3-O)(mu-4-CHO-pz)3}2(mu-3,5-Ph 2-pz)3] ·H2O·CH2Cl 2, and (PPN)[{Cu3(mu3-O)(mu-4-CNH-pz) 3}2(mu-3,5-Ph2-pz)3].;A one-electron oxidation process has been observed during cyclic voltammetric experiments of complexes with formula [Cu3(mu3-O)(mu-4-R-pz) 3X3]n. The tunable oxidation to a Cu II2CuIII (Cu7+) mixed-valent state has been proven to be easier for (PPN)2[Cu3(mu 3-O)(mu-pz)3Cl3] (R = H and X = Cl). The intervalence charge transfer (IVCT) transition in the latter complex was used for the first time to classify the mixed-valent state in the trinuclear copper(II)-pyrazolate complexes as a highly delocalized class-III system on the Robin-Day classification system. On the other hand, hexanuclear complexes of general formula (PPN)[{Cu 3(mu3-O)(mu-4-R-pz)3}2(mu-4-R'-3,5-Ph 2-pz)3], with two stacked [Cu3(mu3-O)(mu-4-R-pz) 3]n units and a homovalent Cu36+--Cu 36+ - core, show a tunable oxidation to the mixed-valent Cu37+--Cu36+ (CU 613+) and Cu37+--Cu 37+ products. The comproportionation constants provided evidence of significant electronic communication between the two Cu3 (mu3-O) redox centers.;For the first time, a stoichiometric controlled strategy towards coordination polymers with a [Cu3(mu3-E)]-SBU has yielded by design a dimer-of-trinuclear complexes [{Cu3(mu3-OH)(mu-pz) 3(py)2}2(mu-4,4'-bpy)](CF3SO3) 4, a one-dimensional coordination polymer {[Cu3(mu 3-OH)(mu-pz)3(py)(mu-4,4'-bpy)](CF3SO 3)2·0.5H2O}n, and a three-dimensional coordination polymer {[Cu3(mu3-OH)(mu-pz)3 (mu-4,4'-bpy)1.5](CF3SO3)2· 1.5H2O}n. The topology underlying polymer {[Cu 3(mu3-OH)(mu-pz)3(mu-4,4'-bpy)1.5](CF 3SO3)2·1.5H2O}n represents a 3-connected srs net with a high eight-fold interpenetration factor and four pairs of nets with opposite chirality.;The complexes reported here were characterized by means of X-ray crystallography, EPR, NMR, and IR spectroscopies, UV-vis spectrophotometry, CV, ESI-MS, magnetic susceptibility, TGA, and elemental analysis.